This application claims the priority of Korean Patent Application No. 10-2004-0069987, filed on Sep. 2, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an apparatus for remotely determining a fault of subscriber terminals and a method thereof, and more particularly, to an apparatus by which in a passive optical network (hereinafter referred to as a “PON”) system, a central office remotely determines a fault of subscriber terminals, and a method thereof.
2. Description of the Related Art
A PON system has a structure in which an optical line terminal (OLT) 101 is located at a central office 10, and connected to a remote node (RN) 11 through optical fibers, and then, connected to the optical network terminal (ONT) 12 or an optical network user (ONU) terminal of each subscriber through optical fiber. At this time, when time division multiplexing (TDM) or sub-carrier multiplexing (SCM) is applied, an optical power splitter is used as an RN, and when wavelength division multiplexing is applied, an optical filter for WDM is used as an RN.
According to an employed communication protocol and network structure, the PON system is broken down into an Ethernet-PON, an ATM-PON, a WDM-PON, a G-PON, a Super-PON, and so on.
In a PON, since a subscriber terminal is located in a range reaching tens of kilometers away from a central office, it is needed to diagnose (determine) remotely whether there is a fault (failure) in a subscriber terminal. In a PON, multiple subscriber terminals share an upstream communication channel, and if any one terminal among the subscriber terminals goes out of order and upward transmits an abnormal signal outside the assigned time slot, other normal subscriber terminals cannot transmit a normal signal to the central office, either. In this case, there arises a problem that in order to identify the fault subscriber terminal, the network operators should examine each subscriber terminal scattered in a range reaching tens of kilometers.
In order to solve this problem, many methods have been suggested. As the examples, optical time domain reflectometry (OTDR) method (U.S. Pat. No. 6,396,575) and an Operation & Administration & Management (OAM) protocol have been known.
The OTDR is a method by which after a central office transmits a short pulse through an optical line network, the back-scattered pulse (Rayleigh back-scattering) is analyzed to check whether there is a fault on the optical lines of the PON. This method has a limit that only whether or not there is a fault in optical lines is examined and a fault in a subscriber terminal cannot be examined.
The method using the OAM protocol is standardized in 2003 IEEE 802.3ah. In this method, by exchanging OAM protocol data unit (OAMPDU) packets capable of performing the OAM function between the central office and subscriber terminals, it is examined whether or not there is a fault in a subscriber terminal.
However, this method cannot be used when the exchanges of normal OAMPDU packets are impossible due to the serious fault situation, for an example, the assigned-time-slot violation cases.